1. Field of the Invention
This invention relates to direct current (DC) to DC voltage converters. More specifically, this invention relates to saturable core DC to DC voltage converters.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
Magnetic coupled multivibrators are circuit networks designed to convert a direct current (DC) voltage at one level to a DC voltage at another level. In these networks, an input DC voltage is typically transformed into a load current of alternating polarity. Rectification of the associated load waveform yields a DC voltage of generally larger magnitude than the input voltage.
The transistors in conventional multivibrators operate exclusively as switches. The energy required to operate the transistor switches is provided by a feedback winding operatively coupled to a magnetic transformer core. The flux within the transformer core is driven to positive and negative saturation on succeeding half cycles inducing an alternating square wave voltage in a voltage transformer. This square wave is either directly delivered to the load or is rectified to a DC voltage having a magnitude predicated on the turns ratio of the voltage transformer.
In applications where the power available to energize the switching transistors is limited, the efficiency of the converter becomes of particular importance. In general, to maximize the efficiency of a power converter under load, the transistors should switch the maximum voltage possible. As a consequence of junction heating within the transistors, there exists a maximum collector current which can be switched independent of supply voltage. It follows that for a given collector current, power output increases directly with supply voltage. Assuming other circuit losses remain constant, the efficiency under load thus increases with increased supply voltage.
Unfortunately, high-power transistors utilized at such elevated supply voltages generally exhibit low current gain. This induces large transistor base currents as a consequence of the substantial collector currents flowing during high-power operation. Such large base currents degrade efficiency by creating high ohmic losses in an input resonant network disposed to drive the transistor switches.
In addition, certain voltage converters rely on external circuitry to trigger initial oscillation within the resonant transistor driver network. This requirement for an ancillary network to induce initial oscillation is often disadvantageous to the extent that the cost and complexity of the voltage converter is increased.
Accordingly, a need in the art exists for a high efficiency DC to DC voltage converter disposed to initiate oscillation without the aid of external circuitry.